using System.Security.Cryptography;

namespace VRage
{
	public class Crc32 : HashAlgorithm
	{
		private const uint DEFAULT_SEED = uint.MaxValue;

		private static readonly uint[] m_crcTable = new uint[256]
		{
			0u, 1996959894u, 3993919788u, 2567524794u, 124634137u, 1886057615u, 3915621685u, 2657392035u, 249268274u, 2044508324u,
			3772115230u, 2547177864u, 162941995u, 2125561021u, 3887607047u, 2428444049u, 498536548u, 1789927666u, 4089016648u, 2227061214u,
			450548861u, 1843258603u, 4107580753u, 2211677639u, 325883990u, 1684777152u, 4251122042u, 2321926636u, 335633487u, 1661365465u,
			4195302755u, 2366115317u, 997073096u, 1281953886u, 3579855332u, 2724688242u, 1006888145u, 1258607687u, 3524101629u, 2768942443u,
			901097722u, 1119000684u, 3686517206u, 2898065728u, 853044451u, 1172266101u, 3705015759u, 2882616665u, 651767980u, 1373503546u,
			3369554304u, 3218104598u, 565507253u, 1454621731u, 3485111705u, 3099436303u, 671266974u, 1594198024u, 3322730930u, 2970347812u,
			795835527u, 1483230225u, 3244367275u, 3060149565u, 1994146192u, 31158534u, 2563907772u, 4023717930u, 1907459465u, 112637215u,
			2680153253u, 3904427059u, 2013776290u, 251722036u, 2517215374u, 3775830040u, 2137656763u, 141376813u, 2439277719u, 3865271297u,
			1802195444u, 476864866u, 2238001368u, 4066508878u, 1812370925u, 453092731u, 2181625025u, 4111451223u, 1706088902u, 314042704u,
			2344532202u, 4240017532u, 1658658271u, 366619977u, 2362670323u, 4224994405u, 1303535960u, 984961486u, 2747007092u, 3569037538u,
			1256170817u, 1037604311u, 2765210733u, 3554079995u, 1131014506u, 879679996u, 2909243462u, 3663771856u, 1141124467u, 855842277u,
			2852801631u, 3708648649u, 1342533948u, 654459306u, 3188396048u, 3373015174u, 1466479909u, 544179635u, 3110523913u, 3462522015u,
			1591671054u, 702138776u, 2966460450u, 3352799412u, 1504918807u, 783551873u, 3082640443u, 3233442989u, 3988292384u, 2596254646u,
			62317068u, 1957810842u, 3939845945u, 2647816111u, 81470997u, 1943803523u, 3814918930u, 2489596804u, 225274430u, 2053790376u,
			3826175755u, 2466906013u, 167816743u, 2097651377u, 4027552580u, 2265490386u, 503444072u, 1762050814u, 4150417245u, 2154129355u,
			426522225u, 1852507879u, 4275313526u, 2312317920u, 282753626u, 1742555852u, 4189708143u, 2394877945u, 397917763u, 1622183637u,
			3604390888u, 2714866558u, 953729732u, 1340076626u, 3518719985u, 2797360999u, 1068828381u, 1219638859u, 3624741850u, 2936675148u,
			906185462u, 1090812512u, 3747672003u, 2825379669u, 829329135u, 1181335161u, 3412177804u, 3160834842u, 628085408u, 1382605366u,
			3423369109u, 3138078467u, 570562233u, 1426400815u, 3317316542u, 2998733608u, 733239954u, 1555261956u, 3268935591u, 3050360625u,
			752459403u, 1541320221u, 2607071920u, 3965973030u, 1969922972u, 40735498u, 2617837225u, 3943577151u, 1913087877u, 83908371u,
			2512341634u, 3803740692u, 2075208622u, 213261112u, 2463272603u, 3855990285u, 2094854071u, 198958881u, 2262029012u, 4057260610u,
			1759359992u, 534414190u, 2176718541u, 4139329115u, 1873836001u, 414664567u, 2282248934u, 4279200368u, 1711684554u, 285281116u,
			2405801727u, 4167216745u, 1634467795u, 376229701u, 2685067896u, 3608007406u, 1308918612u, 956543938u, 2808555105u, 3495958263u,
			1231636301u, 1047427035u, 2932959818u, 3654703836u, 1088359270u, 936918000u, 2847714899u, 3736837829u, 1202900863u, 817233897u,
			3183342108u, 3401237130u, 1404277552u, 615818150u, 3134207493u, 3453421203u, 1423857449u, 601450431u, 3009837614u, 3294710456u,
			1567103746u, 711928724u, 3020668471u, 3272380065u, 1510334235u, 755167117u
		};

		private uint m_crcValue;

		public uint CrcValue => (uint)((base.HashValue[0] << 24) | (base.HashValue[1] << 16) | (base.HashValue[2] << 8) | base.HashValue[3]);

		public override int HashSize => 32;

		public override void Initialize()
		{
			m_crcValue = 0u;
		}

		protected override void HashCore(byte[] buffer, int start, int length)
		{
			m_crcValue ^= uint.MaxValue;
			while (--length >= 0)
			{
				m_crcValue = m_crcTable[(m_crcValue ^ buffer[start++]) & 0xFF] ^ (m_crcValue >> 8);
			}
			m_crcValue ^= uint.MaxValue;
		}

		protected override byte[] HashFinal()
		{
			base.HashValue = new byte[4]
			{
				(byte)((m_crcValue >> 24) & 0xFFu),
				(byte)((m_crcValue >> 16) & 0xFFu),
				(byte)((m_crcValue >> 8) & 0xFFu),
				(byte)(m_crcValue & 0xFFu)
			};
			return base.HashValue;
		}

		public Crc32()
			: this()
		{
		}
	}
}
